1. Field of the Invention
The present invention relates to a method and an apparatus for receiving digital broadcast signals, for example, digital satellite broadcast signals.
2. Description of the Related Art
As television broadcast systems using geostationary satellites, digital broadcast systems, as well as analog broadcast systems, are coming into use. In the digital broadcast system, signals representing a plurality of television programs compressed according to, for example, the Moving Picture Experts Group (MPEG) method, can be multiplexed onto a single carrier and then be provided.
In a digital broadcast receiving apparatus, a user selects a carrier including the multiplexed television broadcast program that the user would like to audio-visually observe. The selected carrier is then demodulated, thereby obtaining a transport stream in which compressed data representing a plurality of television broadcast programs are multiplexed.
The compressed data of the target television broadcast program is then extracted from the transport stream. The extracted compressed data is decompressed, and an analog output video signal and an analog output audio signal are formed from the decompressed digital data. Images and sound of the target television broadcast program are reproduced from the analog output video signal and the analog output audio signal, respectively.
The above type of digital broadcast receiving apparatus is provided with a digital interface. Through this interface, a transport stream in which compressed data representing a plurality of broadcast programs are multiplexed can be supplied to and recorded on, for example, a digital video tape recorder (hereinafter referred to as the “DVTR”). Also, the recorded transport stream can be supplied from the DVTR to the digital broadcast receiving apparatus, and a television broadcast program contained in the supplied transport stream can be audio-visually observed by using the digital broadcast receiving apparatus.
As discussed above, transport streams are supplied to and received from the digital interface of the digital broadcast receiving apparatus. Accordingly, it is impossible to record and reproduce broadcast program signals output through the digital interface by using only an apparatus that is not provided with a compression/decompression function compatible with a compression method used in digital broadcasting.
For example, it is now assumed that a broadcast program signal provided by digital broadcasting has been recorded on a video tape with a DVTR connected to a digital broadcast receiving apparatus installed in a living room. Such a signal cannot be reproduced by a DVTR installed in another room that is neither connected to a digital broadcast receiving apparatus nor provided with a compression/decompression function compatible with the digital broadcast data compression method.
As noted above, the digital interface of the digital broadcast receiving apparatus supplies and receives transport streams. Thus, signals compressed by the MPEG method that are normally used in broadcasts cannot be recorded on a recording medium through this digital interface. For example, by using a recording/reproducing apparatus that uses as a recording medium a small magneto-optical disc, which is referred to as an MD, having a compression format different from the MPEG method (this apparatus will hereinafter be referred to as a “MD unit”), it is not possible to record on the MD only digital audio signals of a target music program or an education program concerning, for example, English conversation.
As described above, in most cases, the transport streams transmitted and received through the digital interface of a digital broadcast receiving apparatus cannot be utilized without the digital broadcast receiving apparatus. Accordingly, it is not possible to record or reproduce only a target broadcast program on or from a recording medium by using various digital external units, such as a DVTR and an MD unit.